U.S. patent number 5,530,963 [Application Number 08/168,693] was granted by the patent office on 1996-06-25 for method and system for maintaining routing between mobile workstations and selected network workstation using routing table within each router device in the network.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Victor S. Moore, Richard G. Van Duren, David C. Wu.
United States Patent |
5,530,963 |
Moore , et al. |
June 25, 1996 |
Method and system for maintaining routing between mobile
workstations and selected network workstation using routing table
within each router device in the network
Abstract
A method and system for maintaining a routing path between a
selected workstation within a multisegment local area network and a
mobile workstation wherein individual segments within the
multisegment local area network are interconnected by a router
device and wherein selected segments within the multisegment local
area network include radio frequency transceivers adapted to
provide a wireless communications link with mobile workstations.
Each time communication is established between a mobile workstation
and a selected workstation within the multisegment local area
network via a radio frequency transceiver a routing table entry is
established which identifies a segment location for the mobile
workstation within a routing table associated with each router
device within the multisegment local area network. A routing table
entry is also established which identifies a segment location for
the selected workstation within the routing table associated within
each router device within the multisegment local area network in
response to each attempt at establishment of communication between
the selected workstation and the mobile workstation. Thereafter,
all routing table entries which identify the segment location for a
mobile workstation are automatically deleted in response to a
termination of communications between the mobile workstation and
the radio frequency transceiver. Routing path determination for
communications between a mobile workstation and any workstation
within the multisegment local area network may then be determined
by reference to a routing table associated with each router device
within a multisegment local area network without requiring the
maintenance of routing path information at each workstation within
the multisegment local area network.
Inventors: |
Moore; Victor S. (Delray Beach,
FL), Van Duren; Richard G. (Big Torch Key, FL), Wu; David
C. (Boca Raton, FL) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
22612547 |
Appl.
No.: |
08/168,693 |
Filed: |
December 16, 1993 |
Current U.S.
Class: |
709/243;
370/351 |
Current CPC
Class: |
H04W
40/246 (20130101); H04L 12/4604 (20130101); H04L
45/54 (20130101); H04W 40/20 (20130101) |
Current International
Class: |
H04L
12/28 (20060101); H04L 12/46 (20060101); G06F
013/00 () |
Field of
Search: |
;395/200,200.2,200.09,200.12,200.15 ;370/85.1,95.1 ;379/59
;455/33.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
0475865A2 |
|
Mar 1992 |
|
EP |
|
0483546A1 |
|
May 1992 |
|
EP |
|
Primary Examiner: Lee; Thomas C.
Assistant Examiner: Meky; Moustafa Mohamed
Attorney, Agent or Firm: Tomlin; Richard A. Dillon; Andrew
J.
Claims
We claim:
1. A method for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation, wherein individual segments within said multisegment
local area network are each interconnected utilizing a router
device and wherein selected individual segments of said
multisegment local area network include a radio frequency
transceiver adapted to communicate with said mobile workstation,
said method comprising the steps of:
coupling said mobile workstation to said multisegment local area
network in response to an initiation of communication between said
mobile workstation and a selected radio frequency transceiver
within a segment within said multisegment local area network;
establishing a routing table only within each router device;
automatically establishing a routing table entry which identifies a
location of said mobile workstation within a routing table
associated with each router device within said multisegment local
area network in response to an attempted initiation of
communication between said mobile workstation and a selected
workstation within said multisegment local area network;
automatically establishing a routing table entry which identifies a
location of said selected workstation within a routing table
associated with each router device within said multisegment local
area network in response to an attempted initiation of
communication between said selected workstation and said mobile
workstation; and
automatically deleting each routing table entry which identifies a
location of said mobile workstation within each routing table
associated with a router device within said multisegment local area
network in response to a termination of communication between said
mobile workstation and said selected radio frequency transceiver by
transmitting an address delete request to each router device within
said multisegment local area network from said selected radio
frequency transceiver in response to a termination of communication
between said mobile workstation and said selected radio frequency
transceiver, wherein a routing path between said selected
workstation and said mobile workstation may be determined from a
routing table associated with each router device within said
multisegment local area network without requiring the maintenance
of routing path information at each workstation within a set
multisegment local area network.
2. The method for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation according to claim 1, wherein said step of
automatically establishing a routing table entry which identifies a
location of said mobile workstation within a routing table
associated with each router device within said multisegment local
area network further comprises the step of establishing a routing
table entry which identifies a segment location for said mobile
workstation and a proposed destination segment location for said
selected workstation within a routing table associated with each
router device within said multisegment local area network in
response to an attempted initiation of communication between said
mobile workstation and said selected workstation.
3. The method for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation according to claim 1, wherein said step of
automatically establishing a routing table entry which identifies a
location of said selected workstation within a routing table
associated with each router device within said multisegment local
area network further comprises the step of establishing a routing
table entry which identifies a segment location for said selected
workstation and a proposed destination segment location for said
mobile workstation within a routing table associated with each
router device within said multisegment local area network in
response to an attempted initiation of communication between said
selected workstation and said mobile workstation.
4. A system for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation, wherein individual segments within said multisegment
local area network are each interconnected utilizing a router
device and wherein selected individual segments of said
multisegment local area network include a radio frequency
transceiver adapted to communicate with said mobile workstation,
said system comprising:
means for establishing a routing table only within each router
device;
means for coupling said mobile workstation to said multisegment
local area network in response to an initiation of communication
between said mobile workstation and a selected radio frequency
transceiver within a segment within said multisegment local area
network;
means for automatically establishing a routing table entry which
identifies a location of said mobile workstation within a routing
table associated with each router device within said multisegment
local area network in response to an attempted initiation of
communication between said mobile workstation and a selected
workstation within said multisegment local area network;
means for automatically establishing a routing table entry which
identifies a location of said selected workstation within a routing
table associated with each router device within said multisegment
local area network in response to an attempted initiation of
communication between said selected workstation and said mobile
workstation; and
means for automatically deleting each routing table entry which
identifies a location of said mobile workstation within each
routing table associated with a router device within said
multisegment local area network in response to a termination of
communication between said mobile workstation and said selected
radio frequency transceiver by transmitting an address delete
request to each router device within said multisegment local area
network from said selected radio frequency transceiver in response
to a termination of communication between said mobile workstation
and said selected radio frequency transceiver, wherein a routing
path between said selected workstation and said mobile workstation
may be determined from a routing table associated with each router
device within said multisegment local area network without
requiring the maintenance of routing path information at each
workstation within a set multisegment local area network.
5. The system for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation according to claim 4, wherein said means for
automatically establishing a routing table entry which identifies a
location of said mobile workstation within a routing table
associated with each router device within said multisegment local
area network further comprises means for establishing a routing
table entry which identifies a segment location for said mobile
workstation and a proposed destination segment location for said
selected workstation within a routing table associated with each
router device within said multisegment local area network in
response to an attempted initiation of communication between said
mobile workstation and said selected workstation.
6. The system for maintaining a routing path between a selected
workstation within a multisegment local area network and a mobile
workstation according to claim 4, wherein said means for
automatically establishing a routing table entry which identifies a
location of said selected workstation within a routing table
associated with each router device within said multisegment local
area network further comprises means for establishing a routing
table entry which identifies a segment location for said selected
workstation and a proposed destination segment location for said
mobile workstation within a routing table associated with each
router device within said multisegment local area network in
response to an attempted initiation of communication between said
selected workstation and said mobile workstation.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to improved communication
within a multisegment local area network and in particular to
improved communication within a multisegment local area network
which includes mobile workstations which are coupled to the network
via radio frequency transceivers. Still more particularly, the
present invention relates to improved communication within a
multisegment local area network which includes mobile workstations
without requiring the maintenance of routing path information at
each workstation within the network.
2. Description of the Related Art
Computer networks are increasingly common in the modern workplace.
Such networks typically include multiple workstations and host or
server devices which may be distributed over a vast geographic
distance. Many different network topologies exist for
interconnecting multiple computers into a distributed data
processing system. One common technique for interconnecting
multiple computers within a data processing network is the
so-called Token Ring local area network environment. The Token Ring
network environment is defined by the IEEE 802.5 standard and is
well known to those having ordinary skill in the art.
In a Token Ring local area network environment, the path which data
travels from one workstation to another workstation or host/server
device, is established during initialization. This path is normally
established by a discovery process utilizing "broadcast" messages,
such as TESTS or XID. A Token Ring bridge or router device builds a
path on which the broadcast frame travels by concatenating the
router address with the routing information field of the broadcast
messages. Thus, once a path has been established, it will not
change during the duration of the communication session between
elements within the network. If for some reason the path is
disconnected during a communication session, the session must be
terminated and a new path reestablished by re-initiating the
session.
In other local area networks, devices within the network are
interconnected utilizing router devices which maintain knowledge of
all network interconnections. That is, the path required to
traverse the network from one workstation to a second workstation,
or host/server device. The logical name of a server device or
workstation normally includes both the unit identification and the
network identification in which the system or station is connected.
During station initialization a broadcast message is also utilized
to establish a path between the initializing station and the
targeted system. The router device utilizes the network
identification as part of the station address in order to establish
a path between stations. Again, once a path is established it
remains unchanged during the entire communications session.
Mobile or remote workstations are often interconnected into such
networks utilizing so-called "dial up" facilities. Such
workstations "call up" a local area network Gateway entity through
a Public Switched Telephone Network (PSTN). As above, once such a
connection has been made, the path between the workstation and the
connecting host is fixed for the duration of the communications
session. A mobile workstation may be allowed to relocate within the
Public Switched Telephone Network (PSTN), utilizing systems which
permits variance in the portion of the link from the mobile
workstation to a local cellular receiving station. See for example,
U.S. Pat. No. 4,984,247 and U.S. Pat. No. 4,901,340. A new
connection and session must be reestablished if the workstation
moves to a different location which alters the location of the link
with the Public Switched Telephone Network (PSTN).
In a modern multisegment local area network, mobile workstations
may be connected to host system or other workstations within the
network through a radio frequency transceiver station. In a manner
similar to that utilized in a cellular telephone system when the
mobile workstation travels throughout the network environment, the
interconnection with the mobile workstation may be changed from one
radio frequency transceiver station to a second radio frequency
transceiver station. In prior art system this requires the
connecting path between the host system or workstation and the
mobile workstation to be altered, dependent upon the new location
of the mobile workstation.
Local area networks which utilize wireless connections without
accessing a Public Switched Telephone Network (PSTN) are often
established within corporate offices, college campuses or other
similar locations. Thus, it should be apparent that a method and
system whereby a mobile workstation may maintain a routing path to
a host/server device or other workstation despite relocation within
a multisegment local area network would be highly advantageous.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide
improved communication within a multisegment local area
network.
It is another object of the present invention to provide improved
communication within a multisegment local area network which
includes mobile workstations which are coupled to the network via
radio frequency transceivers.
It is yet another object of the present invention to provide
improved communication within a multisegment local area network
which includes mobile workstations without requiring the
maintenance of routing path information at each workstation within
the network.
The foregoing objects are achieved as is now described. The method
and system of the present invention may be utilized to maintain a
routing path between a selected workstation within a multisegment
local area network and a mobile workstation wherein individual
segments within the multisegment local area network are
interconnected by a router device and wherein selected segments
within the multisegment local area network include radio frequency
transceivers adapted to provide a wireless communications link with
mobile workstations. Each time communication is established between
a mobile workstation and a selected workstation within the
multisegment local area network via a radio frequency transceiver a
routing table entry is established which identifies a segment
location for the mobile workstation within a routing table
associated with each router device within the multisegment local
area network. A routing table entry is also established which
identifies a segment location for the selected workstation within
the routing table associated within each router device within the
multisegment local area network in response to each attempt at
establishment of communication between the selected workstation and
the mobile workstation. Thereafter, all routing table entries which
identify the segment location for a mobile workstation are
automatically deleted in response to a termination of
communications between the mobile workstation and the radio
frequency transceiver. Routing path determination for
communications between a mobile workstation and any workstation
within the multisegment local area network may then be determined
by reference to a routing table associated with each router device
within a multisegment local area network without requiring the
maintenance of routing path information at each workstation within
the multisegment local area network.
The above as well as additional objectives, features, and
advantages of the present invention will become apparent in the
following detailed written description.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set
forth in the appended claims. The invention itself, however, as
well as a preferred mode of use, further objectives and advantages
thereof, will best be understood by reference to the following
detailed description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a pictorial representation of a multisegment local area
network which includes at least one mobile workstation which may be
utilized to implement the method and system of the present
invention;
FIG. 2 is a high level block diagram of a device driver which may
be utilized to link a mobile workstation with a multisegment local
area network in accordance with the method and system of the
present invention;
FIG. 3 is a high level block diagram of a router device which may
be utilized to interconnect segments of the multisegment local area
network of FIG. 1 in accordance with the method and system of the
present invention;
FIG. 4 is a pictorial representation of a Token Ring Frame Format
which may be utilized to implement the method and system of the
present invention;and
FIG. 5A-5D are pictorial representations of the maintenance of
routing paths within routing tables in each router device within
the multisegment local area network of FIG. 1 in accordance with
the method and system of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
With reference now to the figures and in particular with reference
to FIG. 1, there is depicted a pictorial representation of a
multisegment local area network 10 which includes at least one
mobile workstation which may be utilized to implement the method
and system of the present invention. As illustrated, multisegment
local area network 10 includes a plurality of local area network
segments 12, 14 and 16. Disposed at various points throughout
multisegment local area network 10 are various computer devices
such as host/servers 18, 20, and 22. Additionally, workstations
such as workstations 24 and 26 may also be present in large numbers
within multisegment local area network 10.
As those skilled in the art will appreciate upon reference to the
foregoing, multiple segments within multisegment local area network
10 are typically interconnected utilizing a router device, such as
router devices 28 and 30. Typically, a router device includes a
ring station on each ring to which that router device is attached.
The router device copies communication frames destined for other
segments within the multisegment local area network and transmits
communication frames from other segments destined for the local
segment. Router device 28 and 30 may be implemented utilizing any
appropriately programmed computer such as the International
Business Machines Corporation PS/2 computer.
Also coupled to various segments within multisegment local area
network 10 are radio frequency transceivers 32 and 34. In the
manner described above, radio frequency transceivers 32 and 34 make
it possible for mobile workstations which include radio frequency
communication devices to freely move throughout the areas serviced
by multisegment local area network 10. Radio frequency transceivers
32 and 34 may be implemented utilizing existing equipment such as
the Range LAN, manufactured by Proxim. Mobile workstation 36, which
may be implemented utilizing any suitable portable computer which
includes radio frequency communications capability, such as the
HP100, manufactured by Hewlett-Packard Company, may be utilized
anywhere within the effective range of radio frequency transceiver
devices 32 and 34 and, in accordance with the method and system of
the present invention, a routing path between mobile workstation 36
and a selected workstation or host/server device will be
maintained.
Referring now to FIG. 2, there is depicted a high level block
diagram of a device driver which may be utilized to link mobile
workstation 36 of FIG. 1 with a multisegment local area network in
accordance with the method and system of the present invention.
Device driver 38 is a Medium Access Control (MAC) sub-layer. Device
driver 38 is thus written according to the operating system
dependent local area network (LAN) driver interface, such as NDIS.
Thus, to mobile workstation 36 device driver 38 presents a Token
Ring (IEEE Standard 802.5) appearance.
Device driver 38 also includes command processor 42, data frame and
buffer manager 44 and radio frequency physical frame delivery
segment 48. Each of these segments operates in a manner well known
to those having ordinary skill in the art. In accordance with an
important feature of the present invention device driver 38 also
includes a registration and hand off control 46 which provides the
registration process between mobile workstation 36 and a radio
frequency transceiver, as well as controlling the "hand off"
sequences as a mobile workstation moves from one radio frequency
transceiver to a second radio frequency transceiver.
In accordance with the method and system of the present invention,
registration and hand off control 46 utilizes various primitives
between registration and hand off control 46 and device driver 38.
These primitives have local significance and are based in part,
upon the operating environment and functional capability of device
driver 38. These primitives, which will be described in greater
detail herein, include: Open.request; Open.confirm; Close.request;
Close.confirm; close.indicates; Add.sub.-- Group.sub.--
Address.request; Deleted.sub.-- Group.sub.-- Address.request; and
Set.sub.-- Functional.sub.-- Address.request.
The primitive "Open.request" provides the radio frequency physical
layer and the radio frequency transceiver with the "Physical unit"
address of mobile workstation 36. This primitive defines the
registration process from device driver 36 to registration and hand
off control 46. This primitive enables mobile workstation 36 to
broadcast its presence to any radio frequency transceiver within
multisegment local area network 10. This primitive takes the
form:
______________________________________ Open.request { TR.sub.--
unit.sub.-- address } ______________________________________
The "TR.sub.-- unit.sub.-- address" parameter specifies the
individual Token Ring entity address. This parameter is a six byte
field which is defined by the IEEE 802.5 Standard. This primitive
will be generated when registration and hand off control 46
broadcasts a "Registration Request" message to any radio frequency
transceiver.
The "Open.confirm" primitive defines the confirmation from
registration and hand off control 46 to device driver 38, whether
or not there is a radio frequency transceiver within range of
mobile workstation 36. This primitive takes the form:
______________________________________ Open.confirm { Open.sub.--
status } ______________________________________
The "Open.sub.-- status" parameter defines either a positive or
negative status, based upon the availability of a receiving radio
frequency transceiver. If the status is positive, mobile
workstation 36 is enabled. If the response status is negative,
device driver 38 will begin a recovery or retry process. This
primitive is generated in response to an "Open.sub.-- request" from
device driver 38.
Next, the "Close.request" primitive is utilized to remove the
address of a local station from all radio frequency transceivers
within multisegment local area network 10. A station thus
identified is disabled from sending or receiving any messages
within multisegment local area network 10. All Group and Functional
addresses defined by this station will be deleted from all radio
frequency transceivers within multisegment local area network 10.
This primitive takes the form:
______________________________________ Close.request { TR.sub.--
unit.sub.-- address } ______________________________________
The "TR.sub.-- unit.sub.-- address" parameter specifies the
individual Token Ring entity address which was specified in the
"Open.request" primitive. This primitive is generated when
registration and hand off control 46 broadcasts a "DE-Register
Request" message to any radio frequency transceiver within
multisegment local area network 10. After this message is received
by a radio frequency transceiver within multisegment local area
network 10, the radio frequency transceiver will delete that
station's Unit Address; Associated group and Functional addresses
from its routing table.
The "Close.confirm" primitive defines the confirmation from
registration and hand off control 46 to device driver 38 that the
physical unit is disabled from sending or receiving any messages.
This primitive takes the form:
______________________________________ Close.confirm { Close.sub.--
status } ______________________________________
Wherein the "Close.sub.-- status" always defines a positive status.
This primitive is generated in response to a Close.sub.-- request
from device driver 38.
Next, the "Close.indicate" primitive defines to device driver 38
that the station is moving out of range of any radio frequency
transceivers and that the physical radio frequency disconnection
will be disconnected. The station is thus closed. That station
address, its Group and Functional addresses will be deleted from
all radio frequency transceivers within multisegment local area
network 10. This primitive takes the form:
______________________________________ Close.indicate { }
______________________________________
This primitive is generated when registration and hand off control
46 determines that a mobile workstation 36 is now out of the range
of any radio frequency transceivers within multisegment local area
network 10. Registration and hand off control 46 will then reset
the physical adapted and all software parameters. Device driver 38
must thereafter issue an "Open.request" in order to reestablish
radio frequency connections.
The "Add.sub.-- Group.sub.-- Address" request primitive defines a
Group (Multicast) address and allows the station to respond to this
address. This primitive takes the form:
______________________________________ Add.sub.-- Group.sub.--
Address.request { Group.sub.-- Address }
______________________________________
Wherein the "Group.sub.-- Address" parameter is a six byte field
which is defined by the IEEE 802.5 Standard. This primitive is
generated in response to registration and hand off control 46
generating a "RF.sub.-- Add.sub.-- Group.request" to a radio
frequency transceiver in order to inform the transceiver to decode
this address as part of mobile workstation 36's profile.
Next, the "Delete.sub.-- Group.sub.-- Address.request" primitive is
utilized to remove the Group (Multicast) address and forbid that
station to respond to this address. This primitive takes the
form:
______________________________________ Delete.sub.-- Group.sub.--
Address.request { Group.sub.-- Address }
______________________________________
Wherein the "Group.sub.-- Address" parameter is a six byte field
which is defined by the IEEE 802.5 Standard. This primitive is
generated in response to registration and hand off control 46
generating a "RF.sub.-- Delete.sub.-- Group.request" to a radio
frequency transceiver in order to inform the transceiver to remove
this address from the profile of mobile workstation 36.
Finally, the "Set.sub.-- Functional.sub.-- Address.request"
primitive defines the Functional address and allows the station to
respond to that address. This primitive takes the form:
______________________________________ Set.sub.-- Functional.sub.--
Address.request { Functional.sub.-- Address }
______________________________________
Wherein the "Functional.sub.-- Address" parameter is a six byte
field which is defined by the IEEE 802.5 Standard. A "Functional
Address" mask containing al zeroes will reset the
"Functional.sub.-- Address" for a particular station. This
primitive is generated in response to registration and hand off
control 46 generating a "RF.sub.-- Set.sub.-- Functional
Address.request" to the radio frequency transceiver in order to
inform the transceiver to decode this address as part of the
profile of mobile workstation 36.
With reference now to FIG. 3, there is depicted a high level block
diagram of a router device 28 which may be utilized to link a
mobile workstation with a multisegment local area network in
accordance with the method and system of the present invention. As
described above, in a multisegment local area network the segments
within the local area network are interconnected utilizing a router
device. Radio frequency transceivers within a multisegment local
area network are thus interconnected through a series of such
router devices. As a mobile workstation moves from one radio
frequency transceiver location to a second radio frequency
transceiver location, the routing between the radio frequency
transceiver and the connecting workstation or host/server device
must necessarily change. In order to maintain logical connectivity
between a mobile workstation and the host/server device, routing
between the two units must preferably be done in a transparent
manner. In order for normal workstations to coexist in such a
network with mobile workstations which are interconnected utilizing
radio frequency transceiver devices, routing between such devices
must be accomplished utilizing normal architected Token Ring
frames.
Router device 28 is thus interposed between two Token Ring
segments, such as segment 12 and segment 14. Router device 28 thus
includes a ring station on each segment to which the router device
is attached. Thus, ring station 54 is a ring station within segment
12 and ring station 56 is recognized as a ring station within
segment 14. All token ring frames destined for other segments
within multisegment local area network 10 are then copied by router
device 28 and router device 28 also transmits Token Ring frames
from other segments which are destined for a local segment.
In accordance with an important feature of the present invention,
router device 28 includes a dynamic router 58 which is responsible
for address recognition and the construction of a routing table 62
in accordance with an important feature of the present invention.
As illustrated, routing table 62 preferably includes a series of
entries which identify a station address for each station which
originates a Token Ring frame, as well as the identification of the
segment from which that frame originated, an identification of the
segment to which that frame is directed and a so-called "hop" count
which identifies the number of router devices, including the
current router device, through which a particular frame has been
transmitted. In a manner which will be explained in greater detail
herein, routing table 62 may thus be utilized to maintain a routing
path from a mobile workstation to a workstation or host/server
device within multisegment local area network 10 without requiring
the duplication of that routing information at all workstations
within multisegment local area network 10.
Referring now to FIG. 4, there is depicted a pictorial
representation of a Token Ring Frame Format which may be utilized
to implement the method and system of the present invention. This
Token Ring format is defined by the IEEE 802.5 Standard and is
composed of a number of fields which are each one or more bytes in
length. As illustrated, Token Ring format 64 includes an access
control field 66, a frame control field 68, a destination address
field 70 and a source address field 72. A routing information field
74, an information field 76 are optionally provided and not
normally utilized in the prior art Token Ring networks. However, in
accordance with the method and system of the present invention two
special primitives are utilized to establish or remove routing
paths and are included within information field 72. These
primitives are: "DR.sub.-- Routing.sub.-- Request" and "DR.sub.--
Delete.sub.-- Address." Finally, a frame check sequence field 78,
an ending delimiter field 80 and a frame status field 82 are also
provided.
The method and system of the present invention utilizes this normal
architected Token Ring Frame Format and makes certain assumptions
with regard to the network. Firstly, as noted extensively herein,
it is assumed that the network utilizes the IEEE 802.5 Token Ring
protocol. Next, it is assumed that all segments within multisegment
local area network 10 are interconnected utilizing the "Dynamic
Router" technique only and that the Token Ring "Source Routing"
function is not utilized by any station or host/server device.
Further, it is also assumed that all stations are logically
connected on one network and that all station addresses are unique
within that network. There must also be an Active Monitor on each
segment within multisegment local area network 10 and the Dynamic
Routing Function must have a unique Functional Address. There must
also be a Dynamic Routing Manager which assigns and administers
"ring numbers" for each segment connecting to a router device. All
stations within the network must be configured in a hierarchical
topology, that is no loops are permitted and parallel routers
between individual segments of multisegment local area network 10
are not supported. Those skilled in the network art will appreciate
that these assumptions are clearly within the scope and content of
most Token Ring networks which are defined by the IEEE 802.5
Standard.
Next, a series of pseudocode implementations for the various
processes to implement the method and system of the present
invention are illustrated. As described herein each segment within
multisegment local area network 10 may be alternately referred to
as a "ring" and each workstation or host/server device on a segment
as a "ring station." Thus, each time a Token Ring frame of the
format set forth within FIG. 4 arrives at a ring station, dynamic
router 58 of router device 28 will receive that frame and store it
within store and forward buffer 60 (see FIG. 3) and will execute
the following process: ##SPC1##
Next, FIGS. 5A-5D represent pictorial representation of the
maintenance of routing paths within routing tables in each router
device within the multisegment local area network of FIG. 1
utilizing the processes set forth above. Referring to FIG. 1 and
FIG. 5A, if mobile workstation 36 broadcasts a frame and is
initially connected to radio frequency transceiver 32, radio
frequency transceiver 32 will take on the address of mobile
workstation 36, which is presumed to be "0A" for purposes of this
illustration, as the ring station address. Radio frequency
transceiver 32 will then broadcast a Token Ring frame identifying
the originating station address as "0A" and the destination address
as the functional address of host/server device 18. The functional
address of host/server device 18 is for purposes of this
illustration presumed to be "CF."
Next, router device 28 receives that message and makes a
determination that a station address having the identification "0A"
does not currently exist within its routing table. As illustrated
within FIG. 5A, router device 28 builds a routing table 86 which
lists the origination station as "0A" for a frame which originated
in segment 14 and which is directed to segment 12. The "hop" count
for this routing table is listed as "1" since only router device 28
has seen this frame.
Next, router device 28 will forward the DR.sub.-- Routing.sub.--
Request listing the origination station identification as "0A" and
will forward the broadcast message to address "CF." This frame will
then be broadcast onto segment 12. Router 30 will thus receive the
Token Ring frame broadcast by router 28 within segment 12 and upon
discovery that station "0A" is not within its routing table will
build a routing table entry in the manner set forth at reference
numeral 84. That is, the originating station is identified as "0A"
and the segment from which the frame was received is identified as
segment 12. The segment to which the frame was directed is segment
16 and the hop count is set at "2," indicating that both router
device 28 and router device 30 have seen this frame. The request
will be broadcast into segment 16; however, as there are no more
router devices along this path, the frame will be discarded in
accordance with the IEEE 802.5 Standard when it loops back to
router device 30.
Next, the message intended for host/server device 18 having
functional address "CF" is received by host/server device 18, which
acknowledges that broadcast by sending a station to station message
which identifies host/server device 18 as the origination address
and mobile workstation 36 as the destination address. This
acknowledgment will be routed around segment 12 and will be
received by both router device 28 and router device 30. Router
device 30 will examine this acknowledgement and note that the
address listed for host/server device 18 is new. Thus, a routing
table entry will be created within routing table 84 as shown in
FIG. 5B. This new routing table entry identifies host/server device
18 as the origination station and sets forth the origination of
that frame as segment 12 and the destination of that frame through
router device 30 as segment 16. Router device 30 will then
broadcast that frame to segment 16 and after that frame loops
around segment 16 it will be destroyed, as no other router devices
exist within that segment. Router device 30 also will detect the
destination address of mobile workstation 36 within the
acknowledgement message; however, the address from which that
acknowledgement message was received is identical to the address
for mobile workstation 36 presently within routing table 84 and
thus that information will be ignored.
Router device 28 also receives the acknowledgement message and, as
with router device 30 notes that the address for host/server device
18 is new. Thus, a new entry must be created for routing table 86
within router device 28. The new entry within routing table 86 sets
forth the identify of host/server device 18 having its origin
within segment 12 and its destination within segment 14. The frame
is then forwarded to segment 14 and after that frame loops around
segment 14 router device 28 will destroy that message.
Additionally, router device 28 will also find the destination
address for mobile workstation 36 within its routing table and will
thus forward that frame to segment 14.
Next, radio frequency transceiver 32 will receive the forwarded
frame and pass that information on to mobile workstation 36.
Thereafter, communications between mobile workstation 36 and
host/server device 18 may be accurately routed utilizing
information contained within routing table 86 within router device
28.
Next, it is assumed that mobile workstation 36 will move from the
vicinity of radio frequency transceiver 32 to the vicinity of radio
frequency transceiver 34 (see FIG. 1 ). As radio frequency
transceiver 32 detects that mobile workstation 36 is moving out of
its range, it generates a "DR.sub.-- Delete.sub.-- Address" request
with a source address identified as mobile workstation 36 to all
routers within multisegment local area network 10. Radio frequency
transceiver 32 also generates a "RF.sub.-- Hand.sub.--
Off.indicate" to mobile workstation 36. Router devices 28 and 30
each receive the "RF.sub.-- Delete.sub.-- Address" request and will
thus remove all entries from their associated routing tables which
identify mobile workstation 36. Thus, as set forth within FIG. 5C,
the routing table entries for mobile workstation 36 within routing
tables 84 and 86 have been deleted by setting the source address
for that entry to "00."
Next, as mobile workstation 36 attempts communication with radio
frequency transceiver 34 that transceiver will receive a "RF.sub.--
Contact.request" from mobile workstation 36 and the ring station
within radio frequency transceiver 34 will be enabled, identifying
mobile workstation 36 as a station address. The Functional and
Group address are set forth which are enclosed with the "RF.sub.--
Contact.request." Radio frequency transceiver 34 then constructs
and broadcasts a "DR.sub.-- Routing.Request" identifying mobile
workstation 36. As described above, router devices 38 and 30 will
then build a routing table entry as set forth within FIG. 5D which
identifies the origination segment and destination segment for a
frame which originates with mobile workstation 36. As above,
acknowledgements from host/server device 18 will not alter the
routing table entry for that device and thus a routing path for
communication between mobile workstation 36 and host/server device
18 is now completely contained within the routing table associated
with router device 30.
Upon reference to the foregoing those skilled in the art will
appreciate that the method and system of the present invention
provide a technique whereby routing path information for connecting
a mobile workstation with a workstation or host/server device
within a multisegment local area network may be automatically
maintained within each routing device within the multisegment local
area network utilizing a normally architected Token Ring Frame
Format by constructing and altering the routing tables in the
manner set forth herein. Further, this technique obviates any
requirement for maintaining and updating routing information within
each workstation or host/server device within the multisegment
local area network by concentrating that information within a
router device and thus does not require the alteration of the
control applications within the workstation or host/server devices.
In this manner, the routing path information is maintained in a
manner which is entirely transparent to the mobile workstation and
host/server devices.
While the invention has been particularly shown and described with
reference to a preferred embodiment, it will be understood by those
skilled in the art that various changes in form and detail may be
made therein without departing from the spirit and scope of the
invention.
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